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Ground or Alternator?

dreed

Well Known Member
VAF brain trust

I've have an occasional erratic oil temp jumps of 30-50 degrees and right back down. After the initial "hmm" moment the first time followed by a precautionary landing, I narrowed it down to probe, or I think ground. It seems to come and go randomly, sometimes in climb, others in descent and even straight and level with cool air into the cowl with no real correlation to phases of flight.

After a little more thought and research, I think it may be ground or alternator. I went up with a flying buddy so I could test and he could fly. I wanted to test if taking the alternator offline would make a difference.

After getting up to normal op temp, we set up for decent climb rate to maximize load on the engine and to try and get the warning and then I took the alt offline- as soon as I did, the erratic behavior stopped and temp was steady.

I am going to start the conditional in the next week or so, and will check the ground and may add a second. Any thing I should look at on the alternator or other thoughts?

Post of testing- https://youtu.be/O-Y5bibXgmE
 
Dan,

Several moving parts so will need more information. For example:
- Is this a new problem or one that you have always had?
- Any maintenance done before this showed up? Like alternator replacement, engine wiring change, etc.?
- What alternator?
- How are you grounding the engine?
- Any alternator noise in your headphones?

I also note an abnormally high alternator current output (it looks like 22-28amps). For fully charged battery(s) and glass panels steady state current draw should be more like 12 amps. Has it always been this high? If this is a recent change it may point toward a battery going south.

Carl
 
Carl-

thank you, and great questions-

The plane only has about 70 hours now, but I got the first oil temp warning about 15-20 ago or so. Was very sporadic at first, but am now getting it a bit more often, but still not all the time.

No maintenance that seems to correlate with it issue.

Standard (original) plane power alternator

Engine is grounded from case to firewall using very heavy wiring. Standard Vans finishing/wiring kit cabling- but I don't recall the gauge.

No alternator noise at all in headset.

Good catch on the current draw. I am certain we both had our seat warmers on at least low, if not high as it was in the low to mid 30's. Also, this was just a few min after takeoff so maybe a bit of charging still going on, and had wig/wag and other lights on for for sure. I will make sure to double check however on the next flight. The battery is probably 16-18 months old however.

Dan,

Several moving parts so will need more information. For example:
- Is this a new problem or one that you have always had?
- Any maintenance done before this showed up? Like alternator replacement, engine wiring change, etc.?
- What alternator?
- How are you grounding the engine?
- Any alternator noise in your headphones?

I also note an abnormally high alternator current output (it looks like 22-28amps). For fully charged battery(s) and glass panels steady state current draw should be more like 12 amps. Has it always been this high? If this is a recent change it may point toward a battery going south.

Carl
 
I would suspect inadequate grounding between the engine and the airframe/battery. The alternator relies on that ground return path, and if it's not a good solid electrical connection then the engine and alternator will be at a slightly higher voltage potential than the rest of the airframe when the alternator is trying to charge the battery, and that voltage potential is easily picked up by certain sensors attached to the engine, like the oil temp sensor.
 
I would suspect inadequate grounding between the engine and the airframe/battery. The alternator relies on that ground return path, and if it's not a good solid electrical connection then the engine and alternator will be at a slightly higher voltage potential than the rest of the airframe when the alternator is trying to charge the battery, and that voltage potential is easily picked up by certain sensors attached to the engine, like the oil temp sensor.

But - this would be best indicted by slow cranking. Does the engine crank ok?

If the engine is cranking ok, I’d still verify the alternator to engine ground. Usually this is case on case, but perhaps someone added a layer of paint.

Carl
 
Thanks Guys-

Engine cranks great. I'll have the cowl off later this week hopefully, will check all connections, check for paint, add another ground as well just to make sure.
 
Start with the simple

I would test the sender first. I am not sure which sender the AFS has, but I think it’s a resistance based one, so you will have varying resistance values corresponding to temperature.

See these posts to test the Vans type senders, and I bet something similar could be adapted for the Dynon senders.

https://vansairforce.net/community/showpost.php?p=1550086&postcount=3

https://vansairforce.net/community/showthread.php?t=204315


Many times though it comes down to a grounding problem. If it has been getting worse, you might also look for any connection showing signs of corrosion, or buildup. You might also check your main ground wires on the firewall and battery for tightness.
 
I would also bet on grounding in particular as the alternator has only 70 hours on it. If it was a higher time alternator I would actually suspect the alternator itself. Alternators on their way out have all kind of interesting power spikes which can confuse our more modern electronics in interesting (none obvious) ways.... .

Oliver
 
I Concur

I concur with the group that it's a grounding issue. A lack of an adequate ground can do peculiar and sometimes unpredictable things. I've seen skilled technicians at work track down gremlins on sophisticated electronic drives, and even they are sometimes surprised at what one tiny little grounding problem can do.

Double check the crankcase ground, and also confirm your connections to the oil temperature sensor itself. Those are small wires and it's easy to have a loose crimp. Give 'em a good tug to make sure they're crimped well.
 
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